Photovoltaic devices (PV) or solar cells are devices which convert sunlight into direct current (DC) electrical power.
Thin Film based Photovoltaic (TFPV) devices have been using both amorphous silicon film (αSi:H) and microcrystalline silicon film (μCSi:H) for low cost thin film photovoltaic devices. Hydrogenated amorphous silicon (αSi:H) has been studied for applications in solar cells for several decades. More recently, microcrystalline silicon (μCSi:H) has been studied because it is a suitable material for the intrinsic layer in the bottom cell of thin-film tandem solar cells.
The deposition of αSi:H and μCSi:H on large substrate based photovoltaic (PV) panels has been accomplished primarily using silane (SiH4) and hydrogen gases (H2) mixtures. The work have been done in the field includes: US2009/0077805 A1, US2007/0298590 A1), U.S. Pat. No. 6,855,621 B2 and JP2005244037. A. Hammad et al (Thin Solid Films 451-452 (2004) 255-258) studied the hydrogenated microcrystalline silicon thin films using silane (SiH4), hydrogen gases (H2) and disilane (Si2H6).
However, the deposition processes are relatively slow (5 Å/sec for αSi:H and 1-7 Å/sec for μCSi:H) creating a bottle neck in the manufacturing of TFPV panels. This leads to a lower process tool through-put, which in turn leads to higher cost per Watt for the manufactured panels.
Additionally, deposition of αSi:H and μCSi:H on large substrate based photovoltaic (PV) panels with the existing chemistry of SiH4 and H2 yield solar cells with effiClenCles ranging from 6% to 10%, depending, on cell design. The cell effiClency is dependent upon the quality of the αSi:H and μCSi:H deposited, and more speClfically related to the grain size of crystallites in μCSi:H, number of defects and donor impurities present in the film.
Therefore, there is a need of a method for depositing an amorphous silicon film (αSi:H) and a microcrystalline silicon film (μCSi:H) with increased deposition rate and increased cell effiClency.